1. Field
A liquid crystal display and a method for driving the same are provided.
2. Related Art
A liquid crystal display displays a desired image by forming a liquid crystal layer that has an anisotropic dielectric constant on a transparent insulating substrate on the top and bottom sides, adjust the strength of electric fields to change the molecular arrangement of the liquid crystal material and, regulates the amount of liquid transmitted to the transparent insulating substrate.
A thin film transistor liquid crystal display (TFT LCD) using a thin film transistor (TFT) as a switching device is commonly used in electrical appliances. Such a liquid crystal display comprises an LCD panel composed of pixels defined by gate lines and data lines that cross each other and display images. A driver drives the liquid crystal panel. A backlight unit supplies light to the LCD panel.
The backlight unit uses, for example, a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED). The light emitting diode has good power consumption, weight, and brightness, and is used in devices that need to be smaller, thinner and more lightweight.
The backlight unit that uses a light emitting diode as a light source, generally uses a field sequential color (FSC) driving method to get a better picture quality.
The field sequential color (FSC) driving method is a method that displays a color by utilizing an afterimage effect of human eyes by sequentially driving three primary color red, green and blue sources without using red, green blue color filters when displaying a color.
FIG. 1 is a timing chart that explains a method that drives a liquid crystal display of a field sequential color type according to the prior art.
As shown in FIG. 1, in the field sequential color type driving method, one frame on an LCD panel is divided into three sub-frames of red (R), green (G) and blue (B). For example, if the driving frequency is 60 Hz, one frame has a time interval of 16.7 ms, and each frame is divided into sub-frames of red (R), green (G) and blue (B) of 5.56 ms.
Each sub-frame is divided into an addressing period (AP) that writes data by scanning a thin film transistor, a wait period (WP) and a flash period (FP). The addressing period (AP) represents a data writing time. The wait period (WP) represents a LCD response time. The flash period (FP) represents a backlight driving time. The actual flash period (FP) according to each color is a period of time excluding the addressing period (AP) and the wait period (WP). The addressing period (AP) is a gate-on time of all of scan pulses sequentially applied to gate lines of the LCD panel that equals to a value obtained by multiplying a horizontal period for one line (1H period) with the total number of scan lines.
Red, green and blue pixel data of the LCD panel are sequentially generated once in the same ratio (R:G:B=1:1:1) within 1 vertical period, and the backlight unit is also synchronized in the same way to sequentially turn on light sources (light emitting diodes) of red, green and blue.
In the prior art field sequential color type driving method, the timing chart of FIG. 1 is designed such that 1 horizontal period (1H period) is determined in response to one frame, and accordingly a fixed wait period and a flash period are generated in response to the 1 horizontal period.
A design margin for the addressing period and the flash period is small. When 1 horizontal period decreases by a rise in frame frequency, a luminance deviation is generated due to the lack of the wait period, and the picture quality may be degraded due to degradations in color reproduction and contrast ratio (C/R) at a low temperature. The power consumption increases due to an increase of the number of ons and offs of the light emitting diodes. It is difficult to represent a uniform luminance due to flickering.